1. Technical Field of the Invention
The present invention generally relates to a cellular telephone, and more specifically, relates to a cellular telephone used in Code Division Multiple Access (CDMA) system.
2. Description of Related Art
An example of a CDMA cellular telephone system is disclosed in U.S. Pat. No. 5,056,109. In this example, a cellular telephone has transmit power control circuitries 76 and 80 connected in series between a transmit modulator 84 and an antenna 70 and controlled by a control processor 78, so as to control and adjust a power level of transmission power. The control and the adjustment of the power level are required so as to overcome deleterious terrestrial channel fading between a terrestrial base station (a cell-site station) and a mobile unit. The terrestrial channel fading is caused by a path loss in the terrestrial channel, which is on the order of over 80 dB, and the power adjustment at the mobile unit is implemented by a predetermined amount, nominally 1 dB.
The typical standard for the CDMA cellular telephone system enacted in the U.S. is TIA IS-95 (hereinafter IS-95). An example of a transmitter applying IS-95 is shown in FIG. 11. In this example, a modulated signal converted into a transmitting frequency band is supplied to a variable amplitude amplifier 230 and the output of the variable amplitude amplifier 230 is further amplified by a power amplifier means 250 and transmitted to an antenna 450 through a duplexer 400. A controller 380 supplies a gain control signal to the variable amplitude amplifier 230 in order to adjust the gain such that the power transmitted from the antenna 450 will satisfy the required value of transmitting power. The gain control signal is also supplied to a level detecting means 390. The level detecting means 390 supplies a bias signal to the power amplifier means 250 for adjusting the transmitting power. The level detecting means 390 detects a level of the gain control signal, and as shown in FIG. 12, when the level is high (e.g. Gn), it outputs bias value of B2. Then the level decreases, and the level crosses a threshold value, the level detecting means 390 changes the bias abruptly from B2 to B1. Current of the power amplifier means change abruptly when the gain level crosses the threshold value. In IS-95, open-loop power control and closed-loop power control are employed in order to regulate a receiving power at the cell-site station. The open-loop power control, which definitely determines a transmitting power according to an information indicating an intensity of electric field detected by a receiver, does not require a severe accuracy (generally within the range of 9.5 dB). On the other hand, the closed-loop power control performs fine control according to an information indicating a variation of a gain of the signal transmitted from the cell-site station (generally 1 dB step). In this case, the transmitter performs the open-loop power control at first, then it performs the closed-loop power control for the transmitted power to converge into a desired value which the cell-site station requires.
Japanese Patent Laid-open No. Hei-9-46152 discloses a mobile unit including a receiver and a transmitter, where the transmitter has a variable amplitude amplifier for adjusting the power level of the transmission power. In this related art, the mobile unit includes a high frequency power amplifier having a field effect transistor (FET) as an amplifying element, and the variable amplitude amplifier is composed so as to control a bias condition of the FET according to a transmission power. Amount of attenuation according to the transmission power, and gate voltage of the FET corresponding to the amount of attenuation are controlled by degrees, i.e. by 4 dB, according to the predetermined values. When the transmission power is low, the gate voltage is reduced so as to reduce current consumption for prolonging battery life.
A problem in the related art is that the large current consumption shortens the battery life, which shortens the hours of communication on the phone.
Another problem in the related art is that the compensation of the battery life requires an increase of volume and weight of the battery. Further related art is also disclosed in Japanese Patent Application Laid-open Nos. Hei-04-277909 and Hei-06-252797.
It is therefore an object of the present invention to solve the problems of the related art explained above. In view. of the objective of solving the problems explained above, the cellular telephone of the present invention includes an antenna for receiving a first communication signal from a cell-site station and transmitting a second communication signal to the cell-site station, a duplexer connected to the antenna, a receiver connected to the antenna through the duplexer for converting the first communication signal into a voice signal code, and for outputting a signal indicating an intensity of the first communication signal, an encoder/decoder apparatus connected to the receiver and an acoustic transducer for converting the voice signal code into audio signal for driving the acoustic transducer and converting an audio input signal from the acoustic transducer into a input voice code signal, a transmitter connected to the encoder/decoder apparatus and to the antenna through the duplexer for converting the input voice code signal into the second communication signal, and a controller connected to the receiver and the transmitter for controlling amplitude of the transmitter corresponding to the intensity of the first communication signal, wherein the transmitter includes a variable amplitude amplifier and a power amplifier, the controller includes a central processing unit and a memory, the controller controls a gain of the variable amplitude amplifier and a bias condition of the power amplifier according to a function stored in the memory.
In another embodiment, the controller further includes a pulse generator. The pulse generator is connected to the power amplifier so as to supply a pulse as a bias control signal, and the controller controls a pulse width of the pulse so as to control the bias condition.
In a third embodiment, the controller further includes a pulse generator. The pulse generator is connected to the power amplifier so as to supply pulses as a bias control signal, and the controller controls a pulse density of the pulses so as to control the bias condition.
In a fourth embodiment, the power amplifier further includes a smoothing circuit for smoothing the pulse.
In a fifth embodiment, the transmitter further includes a signal generator connected to the controller. The signal generator is connected to the variable amplitude amplifier and the power amplifier so as to supply a gain control signal and a bias control signal to the variable amplitude amplifier and the power amplifier respectively.
The cellular telephone of the present invention also includes an antenna for receiving a first communication signal from a cell-site station and transmitting a second communication signal to the cell-site station, a duplexer connected to the antenna, a receiver connected to the antenna through the duplexer for converting the first communication signal into a voice signal code, and for outputting a signal indicating an intensity of the first communication signal, an encoder/decoder apparatus connected to the receiver and an acoustic transducer for converting the voice signal code into audio signal for driving the acoustic transducer and converting an audio input signal from the acoustic transducer into a input voice code signal, a transmitter connected to the encoder/decoder apparatus and to the antenna through the duplexer for converting the input voice code signal into the second communication signal, and a controller connected to the receiver and the transmitter for controlling amplitude of the transmitter corresponding to the intensity of the first communication signal, wherein the transmitter includes a variable amplitude amplifier and a power amplifier, the power amplifier includes a maximum power detector, the controller includes a central processing unit and a memory, the controller controls a gain of the variable amplitude amplifier according to a function stored in the memory, and the maximum power detector controls an output power of the power amplifier.
As explained above, since the controller controls a gain of the variable amplitude amplifier according to a function stored in the memory, a cellular telephone capable of reducing current consumption is available. In addition, small current consumption enables prolongation of battery life, or use of small-size battery, by which a cellular phone having a long service life or that having a small size is available.